1. Field of the Invention
The present invention generally relates to a method of profile control in metal etching. More specifically, the present invention relates to a method of profile control for etching a metal layer with an anti-reflection layer.
2. Description of the Related Art
In a typical metal-etching process, the overhang (or xe2x80x9cIxe2x80x9d-shape) profile has long been a serious problem, as shown in FIG. 1. Among many disadvantages, voids 20 or empty gaps are often found when depositing dielectric material 18 during the subsequent process to fill between metal lines, as shown in FIG. 2. The incomplete filling can cause possible reliability problems in the IC devices made.
A typical metal layer stacked in semiconductor devices consists of TiN/AlSiCu/TiN/Ti. The overhang (top of xe2x80x9cIxe2x80x9d) is formed because TiN 10 is harder to etch than AlSiCu 12 (mostly Al). Moreover, the bowing at the sidewalls of AlSiCu 12 usually indicates (i) sidewall passivation occurred during the etching process is not enough and (ii) ion bombard is too strong, which knocks off the polymer for sidewall passivation.
Increasing the sidewall passivation can decrease the etch rate at sidewalls and thus forms a tapered metal profile. Such a profile can make the step coverage of the subsequent dielectric material more conformal, less build-up at the top corners of the metal lines, and less void size. In order to protect the Al profile by providing sufficient sidewall passivation, a method that can increase the bias power of the metal etcher is employed. Most of the advanced metal etchers are equipped with separate power sources: top/source power (TP) and bottom/bias power (BP). Roughly speaking, TP pertains to the ion density of plasma to control the isotropic etch rate, and BP pertains to the energy of ion bombard to control the anisotropic etch rate. To provide sufficient sidewall passivation for protecting ALCuSi 12, the bias power BP of the etcher can be increased to bombard photoresist (PR) to form carbonaceous polymers for sidewall passivation. However, it can cause serious loss of PR, which causes metal cutting and is impractical. It is believed that nitrogen (N2) can help forming byproducts, such as BxNy and AlxNy, to protect the sidewalls of the metal layer. However, if [N2] (the flow rate of N2) is too high, it may be difficult to sustain plasma that discharges unstably.
Due to the significant etch rate (ER) difference between TiN and AlSiCu, different etch recipes (i.e. different ER) are used. However, it is often found that there is always a xe2x80x9cdiscontinuityxe2x80x9d occurring at the interface of TiN/AlSiCu. Results are profile (slope) change and xe2x80x9cIxe2x80x9d-shape formation. In the worst case, when etching Al, the originally profile-fixed TiN layer is also affected. Most of all, the xe2x80x9cIxe2x80x9d-shape-free profile is still difficult to maintain with conventional methods.
Therefore, an object of the present invention is to provide a method of profile control for etching a metal layer. The profile of the metal line generated by the present invention has slightly tapered sidewalls, which are formed without xe2x80x9cIxe2x80x9d-shaped metal profile. The voids that may be generated by the subsequent deposition process, therefore, are lessened or disappeared.
The present invention achieves the above-indicated objects by providing a method of profile control for etching a metal layer. The metal layer is positioned on a dielectric layer comprising an aluminum-alloy layer on the dielectric and an anti-reflection layer on the aluminum-alloy layer. The method includes performing a breakthrough step of a first etch recipe to remove the anti-reflection layer and a certain thickness of the aluminum-alloy layer until a predetermined depth is reached. The first etch recipe provides a first source power, a first bias power, and nitrogen as one of the reactive gases. The ratio between the first source power and the first bias power is around 1/3. The method further comprises performing a main etch step of a second etch recipe that has a higher etch rate than the first etch recipe for removing the remaining residue of the metal layer. The second etch recipe provides a second source power, a second bias power, and nitrogen as one of the reactive gases. The ratio between the second source power and the second bias power is about 10/3.
The major advantage of the present invention is that the formation of metal lines with smooth and tapered sidewalls (i.e. xe2x80x9cIxe2x80x9d-shape-free metal profile) can reduce the possibility of forming voids during the subsequent deposition process and thereby improve the reliability of the IC devices made.